1. Field of the Invention
This invention relates to an air-bag arrangement in a car, and more particularly relates to a vent for use in an inflatable curtain cushion arrangement.
2. Technical Background
It is known to provide air-bags in motor vehicles, such as motor cars, which air-bags are adapted to inflate in the event of an accident to provide protection for an occupant of the vehicle. Certain air-bag devices are intended to provide protection in the case of a side impact. Such air-bags are designed to prevent the head of a vehicle occupant from hitting a side window and also to prevent the head of the occupant from emerging through the window opening if the window should be broken or in the lowered position. The air-bag also protects the occupant in the event of vehicle rollover.
Side impact air-bags should be sufficiently rigid to retain the occupant""s head in the vehicle when the window is broken or open. A particular problem arises in ensuring that a lower edge of such an air-bag is sufficiently rigid to prevent the air-bag being pushed out through a window during an accident. Side impact air-bags are usually only a few inches thick when deployed. With only a few inches available to protect vehicle occupants, they are generally more rigid than front-impact air-bags.
Side impact air-bags often remain inflated for a longer period of time than front-impact air bags to provide vehicle occupant protection for longer-duration events, like vehicle rollovers. In contrast, front-impact air bags typically include large vents that allow the inflation gas to escape immediately, even during inflation. Deflation of front-impact air-bags begins immediately after inflation. Thus, front-impact air-bags have immediate venting, while side-impact air-bags require slow or delayed venting. A fully sealed side impact air bag inflates rapidly, but it deflates very slowly, if at all. Fully sealed side impact air bags are not preferred because deflation should occur to facilitate removal of the vehicle occupant(s).
It will be appreciated that there is a need in the art for a vent for use in a sealed inflatable curtain cushion which provides appropriate venting and deflation of the curtain cushion after the inflation event.
The present invention is directed to a venting arrangement for an inflatable curtain cushion. The inflatable curtain cushion is typically connected to a gas generator capable of inflating an inflatable element that forms the curtain cushion. The inflatable element includes first and second fabric layers. Selected parts of the first and second fabric layers are interconnected to define a plurality of cells that are inflated with gas from the gas generator. The first and second fabric layers are themselves gas permeable, but to permit efficient inflation, the fabric layers are preferably coated with a substantially impermeable coating. In a preferred embodiment, the impermeable coating is on the interior surface of fabric layers. Currently preferred coating materials include, but are not limited to, urethanes and silicone/urethanes. Persons skilled in the art will appreciate that other impermeable coatings can be used.
One or more vents are provided in the inflatable element. The vents are defined by a portion of the first and second fabric layers bonded together at the impermeable coating. Because the fabrication bonding to form cells occurs within the interior of the inflatable element, and because the impermeable coating is on the interior of the inflatable element, the vents are formed at points where the impermeable coatings of fabric layers are bonded together. Separation of the bonded first and second fabric layers causes removal or delamination of the coating from one of the fabric layers. Exposure of the underlying uncoated, permeable fabric allows venting of inflation gas. The bonded first and second fabric layers separate when gas pressure within the inflatable element exceeds a threshold pressure.
Various types of fabric bonding can be used to bond the first and second layers together. One currently preferred fabric bonding method is RF (radio frequency) bonding. RF bonding of fabric is well known to persons skilled in the art. For example, inflatable airplane slides, inflatable life jackets, and tents commonly utilize RF bonding of fabric. Other fabric bonding methods include conventional chemical bonding using adhesives and glues.
Regardless of the bonding method used, it is important that the bond between the coating material be stronger than the bond between the coating material and the fabric so that delamination of the coating material from the fabric will occur.
The cells that are inflated with gas from the gas generator are preferably configured to be in gas flow communication with one another. They can be immediately adjacent each other or they can be spaced apart with respect to one another.
In operation, the vent area of exposed, uncoated fabric is preferably in the range from about 20 mm2 to 100 mm2, although this area can vary depending upon the number of vents used. For instance, if only one vent is used, then a larger vent area would be required. But if many vents are used, then each vent can have a smaller vent area. The number and size of vents used can also vary depending upon the permeability of the underlying fabric.
The inflatable element is preferably configured to withstand initial gas inflation pressure within the inflatable element from 100 to 150 KPa. This initial inflation occurs upon side impact or collision. This pressure is typically achieved during a 50 millisecond inflation period. Thereafter, the curtain cushion should maintain an inflation pressure from about 50 to 65 KPa for the next 5 to 10 seconds to protect vehicle occupants from secondary collisions and rollovers. Gas pressure within the inflatable element exceeding about 65 KPa causes separation of the bonded first and second fabric layers at the vents.
It will be appreciated by those having ordinary skill in the art that the force required to delaminate a small area vent is less than the force required to delaminate a large area vent. Also, the force required to cause xe2x80x9cpeelxe2x80x9d delamination is less than the force to cause xe2x80x9cshearxe2x80x9d delamination. Thus, the vent area, the number of vents, and the delamination action can be designed to cause venting at a predetermined inflation pressure.